The tunnel momentum distribution in a magnetic tunnel junction is probed by analyzing the decay
of the hot electrons in the Co metal anode after tunneling, using a three-terminal transistor structure
in which the hot-electron attenuation is sensitive to the tunnel momentum distribution. Solid state
amorphous Al2O3 barriers and the vacuum barrier of a scanning tunneling microscope are
compared. For the former the attenuation length in nominally the same Co is strikingly larger factor
of 2, implying a more isotropic tunnel momentum distribution for Al2O3 barriers.